Waveguide type optical device and method for manufacturing the same

Abstract

A method for fabricating a waveguide type optical device is disclosed, through which a core and a reference plane are obtained at the same time by etching a core layer using a thin layer of a predetermined shape formed on the core layer as a mask. In this waveguide type optical device, the core is easily coupled with an optical element such as an optical fiber by means of the reference plane.

What is claimed is: 
     
       1. A method for fabricating a waveguide optical device comprising the steps of: forming evenly a core layer with a relatively high index of refraction upon an under clad with a relatively low index of refraction;   forming a first and second thin film layers upon said core layer in a core forming region and a reference plane forming region in the vicinity of the core forming region, respectively, said thin film layers having a sufficiently lower etching rate than the etching rate of said core layer;   etching said core layer with said first and second thin film layers used as masks, thereby forming a core and a reference plane, respectively;   removing said first thin film layer on the core;   forming an outer clad with a relatively low index of refraction of a material having a sufficiently higher etching rate than the etching rate of said second thin film layer so as to cover at least said core; and   partially etching said outer clad to expose at least a part of said reference plane.   
     
     
       2. A method according to claim 1, wherein said under clad, said core layer, and said outer clad are formed by heating and vitrifying oxide glass soot whose main component is SiO 2  precipitated by flame hydrolysis; and said first and second thin film layers are formed by sputtering of Si.   
     
     
       3. A method according to claim 2, further comprising the steps of: forming an intermediate layer whose main component is SiO 2  between said core and said outer clad by chemical vapor deposition; and   annealing said intermediate layer by heating the same.   
     
     
       4. A method according to claim 3, wherein said intermediate layer has a thickness within the range from 0.5 to 2 μm. 
     
     
       5. A method according to claim 3, wherein the material gas used in said chemical vapor deposition contains Si(OC 2  H 5 ) 4 . 
     
     
       6. A method according to claim 3, wherein said annealing is performed at a temperature equal to or higher than the heating temperature at which said outer clad is formed. 
     
     
       7. A method according to claim 3, wherein said annealing is performed under a low pressure or in an He atmosphere. 
     
     
       8. A method according to claim 3, wherein said core constitutes an optical coupling portion of a directional optical coupler. 
     
     
       9. A method according to claim 2, wherein said under clad is formed on a Si substrate. 
     
     
       10. A method according to claim 1, further comprising the steps of: fixing an optical element to a guide of a predetermined form having a plane surface to be brought into close contact with said reference plane; and   optically coupling said optical element to said core while said plane surface is in close contact with said reference plane; wherein   said guide is so formed that the optical axis of said optical element aligns with the optical axis of said core when said plane surface is in close contact with said reference plane.   
     
     
       11. A method according to claim 10, wherein said optical element is an optical fiber. 
     
     
       12. A method according to claim 1, wherein two of said second thin film layers are formed on both sides of said first thin film layer so as to face each other across said first thin film layer. 
     
     
       13. A waveguide optical device comprising: an under clad with a relatively low index of refraction;   a core with a relatively high index of refraction formed on said under clad;   an outer clad with a relatively low index of refraction formed so as to cover said core; and   a thin film layer formed in the vicinity of said core on the same plane with the bottom face of said core or on the same plane with the top face of said core; wherein   the top face of said thin film layer is exposed to serve as a reference plane.   
     
     
       14. A waveguide optical device according to claim 13 wherein the main component of said under clad, said core, and said outer clad is SiO 2  and the material of said thin film layer is Si.